1. Field of the Invention
The present invention relates to an optical coupling device for separating and assembling optical signals by using a branched type optical fiber arranged in a case, and more particularly to an optical coupling device for easing optical stress working on the optical fiber.
2. Description of the Prior Art
FIG. 7 shows a plan of an example of optical coupling device according to the prior art.
In the optical coupling device according to the prior art shown in FIG. 7, a plurality of optical fibers are bundled on one end side, and mounted as an internal fiber.
The internal fiber is formed by bundling a plurality of optical fibers on one end side in a state in which the diameters of individual optical fibers are made gradually thinner to equalize the diameters of their end faces to those of an optical fiber to be connected thereto. When optical signals are transmitted from a first end face side of the bundled end of the optical fiber, it is possible at a second end side of the branched optical fibers to separate the optical signals and to let each fiber receive the same optical signals. Or when optical signals are transmitted from at the second end side of the branched optical fibers, it is possible on the first bundled end side to assemble and receive the optical signals.
An optical coupling device 1 shown in FIG. 7 is intended for connection of a plug 11 for use with an F05 type single-core optical fiber connector conforming to Japanese Industrial Standards (JIS)-C-5974 and a plug 12 for use with an F07 type two-core optical fiber connector conforming to JIS-C-5976. In the case 2 of the optical coupling device 1, there are provided a bundled end 3a formed by bundling one end (end on the X1 side in the drawing) of each of two optical fibers and a 1-to-2 branched internal fiber 3 formed by integrating branched ends 3b and 3b formed by branching the other ends of the fibers.
At the one bundled end 3a of the internal fiber 3 is provided a ferrule (holding member) 4, and at the branched ends 3b are provided ferrules (holding member) 5. The ends of the internal fiber 3 are firmly fixed to the ferrules 4 and 5 with an adhesive. The tips of the bundled end 3a and the branched end 3b are fitted in a state in which they barely protrude out of the case 2 from the tips of the ferrules 4 and 5, respectively, and these protruding portions constitute stubs 3a1 and 3b1.
The case 2 is made of synthetic resin. On one end face of the case 2 in the X direction in the drawing is formed a connecting part (connector) 2A, protruding in the X1 direction in the drawing, for connecting the F05 type plug 11, and on the end face is formed a connecting part 2B, protruding in the X2 direction in the drawing, for connecting the F07 type plug 12. To the ends of the connecting parts 2A and 2B of the case are fitted caps 6 and 7. In the caps 6 and 7 are formed through holes 6a, 7a and 7a, respectively.
Tubular sleeve holders 2a, 2b and 2b are formed in the X1-X2 direction in the drawing integrally with the connecting parts 2A and 2B, respectively. Between the inward ends of these sleeve holders 2a and 2b and the caps 6 and 7 are respectively provided the ferrules 4 and 5, respectively, fitted to ends of the internal fiber 3.
On the outer faces of the ferrules 4 and 5 are formed flanges 4a and 5a extending the direction of the external circumference. Between the flanges 4a and 5a on the one hand and the caps 6 and 7 on the other are respectively provided cylindrical coil springs 8, 9 and 9. Therefore, the ferrules 4 and 5 are held within the case 2 in a state in which the inward ends of the sleeve holder 2a and the sleeve holders 2b are pressed in the outward direction by the coil springs 8 and 9. The tips of the ferrules 4 and 5 are set on an optical reference plane Sxe2x80x94S represented by a one-dot chain line in the drawing, and the stubs 3a1 and 3b1 protrude outward from the optical reference plane Sxe2x80x94S.
In the optical coupling device 1, when the F05 type plug 11 is connected to one connecting part 2A, an end face 11a of an optical fiber 11A of the F05 type plug 11 presses an end face of the bundled end 3a in the optical coupling device 1 in a direction toward inside the case 2, with the result that the coil spring 8 is compressed, and the end face of the stub 3a1 is returned to the optical reference plane Sxe2x80x94S. When the F07 type plug 12 is connected to the other connecting part 2B, end faces 12a and 12a of one optical fiber 12A of the F07 type plug 12 press end faces of the branched ends 3b and 3b. Therefore, the coil springs 9 and 9 are compressed in the direction of X1 in the drawing, end faces of the stubs 3b1 and 3b1 are returned to the optical reference plane Sxe2x80x94S.
Thus, when the plug 11 and the plug 12 are fitted, the end face 11a of the optical fiber 11A of the plug 11 presses the end face of the bundled end 3a inward (in the X2 direction), and the end faces 12a and 12a of the optical fibers 12A and 12A of the plug 12 press the end faces of the branched end 3b and 3b of the internal fiber 3 inward (in the X1 direction). This brings both end faces of the optical fibers 11A, 12A and 12A and the end faces of the internal fiber 3 into tight contact with each other to reduce coupling losses of optical energy between the end faces.
However, the conventional optical coupling device 1 described above involves the problem that the connection of the plug 11 for use with the F05 type and of the plug 12 for use with the F07 type causes compressive stresses to work inward on the internal fiber 3 within the case 2 from both ends of the internal fiber 3, and as a result excessive stresses tend to concentrate on the branching portion 3A of the internal fiber 3.
Regarding this problem, the compressive stresses working on the internal fiber 3 can be reduced, and the concentration of stress on the branching portion 3A eased, by increasing the overall length of the internal fiber 3.
However, a greater overall length of the internal fiber 3 means a correspondingly greater overall length of the case 2, which makes it impossible to reduce the size of the optical coupling device 1.
The present invention, attempted to solve the above-noted problems with the prior art, is to provide an optical coupling device permitting alleviation of compressive stresses which would otherwise tend to concentrate on the branching portion of the internal fiber.
Another object of the invention is to provide an optical coupling device permitting a reduction in the overall length of the internal fiber and accordingly in the overall size of the device.
According to the present invention, there is provided an optical coupling device provided in its case with an internal fiber, holding members for holding each of two ends of the internal fiber, first and second connectors each holding one or the other of the holding members shiftably in an axial direction of the internal fiber, and energizing means each energizing, within one or the other connector, the holding member toward a connecting part of the connector, wherein each of the connecting parts of the first and second connectors permits fitting of a plug for holding an external fiber, each connector has within the case a margin of shifting at least toward outside the case, the plug is fitted to the connecting part of the first connector, and the second connector can shift toward outside the case when the first connector is at a limit of inward shifting and a holding member pressed by the plug shifts inward in the case.
Further, when a plug is fitted to the connecting part of the second connector, the second connector reaches a position of shifting limit inward in the case and, when the holding member in the second connector is pressed by the plug to shift inward in the case, the first connector can shift toward outside the case.
Since according to the invention, when plugs are fitted to connectors at the two ends of the optical coupling device, shifting of both connectors together can let compressive stressed generated by energizing members escape, stresses working on the internal fiber can be eased.
In the foregoing configuration, in a state in which plugs are fitted to the first connector and the second connector, the holding member in each of the connectors is shifting inward in the case against an energizing force of the energizing means, and it is preferable for the internal fiber and the external fiber to be pressed by the energizing force.
In the foregoing configuration, since it is possible to adhere closely to each other the end face of the internal fiber and the end face of the optical fiber to be connected thereto, optical signals can be transmitted reliably, and the coupling loss between the optical fibers can also be reduced.
It is preferable that, in the first and second connectors, both of the first connector and second connector can be shifted toward the outside of the case by 2xc3x97xcex4 when the plugs are not fitted, where xcex4 is a quantity of shift of the holding members inward in the case when the plugs are fitted.
It is further preferable that, in a state in which no plug is fitted to either of the connectors, the first connector and second connector are in their respective positions of limit of shifting inward in the case.
In the foregoing configuration, in a state in which plugs are fitted to both connectors, the internal fiber is in a state of free length, and no compressive force works on the internal fiber, and accordingly stresses working on the internal fiber can be eased.
It is also possible to reduce the plays of the two connectors in the case.
Further according to the invention, one of the first and second connectors may be provided with one holding member, a plurality of holding members being provided in the other connector, and the one holding member and the plurality of holding members being connected by the internal fiber to make possible optical separation and optical assembly.